Geochemistry and Genesis of Bedded Cherts in Some Typical Eopaleozoic High Selenium Black Shales, China

Bedded cherts, with varying thickness, are widely distributed in some typical eopaleozoic high Se black shales in China. Bedded cherts are mainly composed of SiO 2 in chemical composition, generally more than 90% with relatively high content of Fe and low content of Mn, Al, Ti. Lithophile elements deplete in cherts, however some elements like As, Ba, Sb, etc., which are typically indicative elements for hydrothermal sedimentation, are rich in cherts. REE distribution pattern show obvious left slope with clearly negative Ce anomaly and slightly positive Eu anomaly. δ 30 Si values of cherts range from -0.7‰ to 1.2‰, and δ 18 O values of cherts range from 17.6‰ to 29.0‰. Above much evidence suggests that origin of bedded cherts mghit be ascribed to hydrothermal sedimentation. At last of the paper, the relationship between hydrothermal cherts and enrichment of Se is discussed. Based on some indirect evidence, it can be concluded that the tectonic environment that hosts cherts should be a prerequisite for the ascension of Se from the deep depth in the crust and for its enrichment at the shallow depth. In the meantime, Si bearing hydrothermal solutions might be a desirable "solvent " for Se.